The comments are a rebuke to Mr Shorten and came as the Opposition Leader prepares to challenge the Prime Minister over climate change policy at Labor's national conference on Friday.

Mr Shorten will place climate policy front and centre, days after unveiling a bold climate policy goal this week that will require half of Australia's large-scale energy production to be generated using renewable sources within 15 years.

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But the Opposition Leader is facing a gruelling three day test of his leadership. Damaging debates over asylum seeker policy, whether or not to bind all MPs to support same-sex marriage and trade policy are among the issues that will test the opposition leader's authority.

Indonesia also expressed its surprise and disappointment on Thursday at Mr Shorten's changed position on boat turn-backs, saying the policy risked lives and shifted the burden of solving people smuggling back on Indonesia.

The Labor Left was mobilising on Thursday over the issue, preparing a formal motion to forbid the ALP from adopting a boat turn-back policy.

One Left MP told Fairfax Media that "we are determined to oppose turn-backs and we have a couple of days to socialise it and work out how it plays out".

But Right faction powerbrokers rallied to Mr Shorten on Thursday, after the Opposition Leader on Wednesday said he wanted the party to adopt the turn-back policy because it "wants to defeat the people smugglers and we want to prevent drownings at sea".

Labor's national platform does not mention the controversial boat turn-backs policy, which the Abbott government has successfully implemented, and the Right believes it could secure up to 215 of the 397 votes to block any Left move to oppose turn-backs.

As a compromise designed to appease the Left, the ALP is also expected to back a move that would double Australia's refugee intake to from 13,750 to 27,000 people over time, as part of a suite of new immigration policies that also includes the abolition of temporary protection visas, and greater transparency and independent oversight of detention centres.

At least one Left faction powerbroker predicted that Mr Shorten would carry the day on the issue.

However, Labor backbencher and former speaker Anna Burke warned voters may abandon the party following Mr Shorten's decision, criticising the Labor leader for pre-empting this weekend's debate and said: "I'm not in a position to support this policy."

She said a genuine regional processing centre was the answer to stop people smugglers, not turning back boats, which would be dangerous for asylum seekers and the Australian navy.

In Indonesia, Andi Rachmianto, the director of international security at Indonesia's department of foreign affairs, said boat turn-backs was against the principle of "burden sharing".

"This kind of policy, the turn-back policy, is unilateral in nature and is shifting the burden back to Indonesia," he said.

"When they are sending back the boats with tens or hundreds of migrants back to Indonesia, to our borders [and travelling as far as] 200 miles, it is risking their lives, especially after they have been already sailing for a few days or one week. This is a humanitarian concern that we would like to underline."

Greens immigration spokeswoman Senator Sarah Hanson-Young said on Thursday that Mr Shorten had "kowtowed" to the Prime Minister's policy of turning back asylum seeker boats. Labor had become a "thin-veiled image of the Liberal Party" particularly on refugees.

Prime Minister Tony Abbott welcomed Mr Shorten's shift on the issue but said that he should have made it years ago.

"I'm prepared to say: good on Bill. I just wish he'd done it two years ago. I just wish he'd done it when he was in government," he said, adding that if Labor had adopted the policy sooner, "up to 1,000 people might not be dead".

"Up to 50,000 people might not have come to Australia illegally by boat. We might not have had the $11 billion budget blow-out that we did because Labor refused to do what was always the right thing here.

He also questioned whether it was a believable switch of policy, because "to make these policies work, you can't just say you support them; you've got to actually believe it in your heart and soul and I'm not sure that too many people in Labor do".